Watercraft



March 10, 1942. R. N. coouuez WATER CRAFT Filed Feb. 11, 1941 PatentedMar. 10, 1942 UNITED STATES PATENT OFFICE I WATERCRAFT Richard NewellCoolidge, Nashville, Tenn.

Application February 11, 1941, Serial No. 378,455

6 Claims.

This invention relates to improvements in water craft, and moreparticularly to steering apparatus for use with screw propelled vessels.It is the general object of the invention to improve the efficiency ofsuch craft by proper dilent fiow, and with substantial uniformity re-.gardless of the angle of helm.

It is generally recognized that the action of a marine propellerconsists essentially of the stern-ward projection of a column of waterwhich is called the propeller race, the change of momentum per unit oftime of this water being equal to the propeller thrust which, duringsteady motion, is balanced by resistance of the vessel. It is alsoappreciated that among the more important losses of energy which occurare the deflection of the propeller race from the proper direction andthe setting up in the race and adjacent water of turbulent fiow.

Serious loss of energy is also caused on the occurrence of thephenomenon known as cavitation, which arises when there is interferencewith the natural flow of water to the screw, resulting in excessiveslip, reduction in thrust, and consequent very greatly reducedefficiency. The diminution of pressure accompanying the acceleration ofwater ahead of the screw may under certain circumstances be sufficientto bring about these conditions.

In its preferred form, the invention contemplates the association withthe screw of dual rudders which are conjointly turned in steering, eachrudder being so shaped as to conform generally to at least a substantialpart of the path described by the propeller tips, and so as to affordgenerally constant clearance with the tips under different angles ofhelm. The rudders, preferably of the balanced type, are further shapedso as to converge toward and diverge away from the propellersufiiciently to compensate for the lateral contraction of theaccelerating race ahead of the propeller in either direction of movementof the vessel, to the extent necessary to prevent serious or disturbingenergy loss by cavitation.

Specifically it is proposed to form the opposed faces of the rudders sothat the intermediate part of each rudder adjacent the propellerdefinesa portion of a surface of revolution of which the axis of generation issubstantially coincident with the rudder axis, and of whichthegeneratrix is a circular are substantially concentric with the circledescribed by the propeller tips and of somewhat greater radius, theopposed rudder faces diverging forward and aft from such intermediateparts. Thus regardless of the direction of movement of the vessel, asufiicient volume of water flows between the leading ends of the ruddersto enable the propeller race to acquire the necessary momentum at thepropeller, and the area between the rudders in the plane of thepropeller,

remains substantially constant when the rudders are concurrently turnedin steering.

Further objects and features will be apparent from the followingdescription, taken in connection with the accompanying drawing, inwhich- Figure 1 is a plan view of a screw propelled vessel illustratingsteering apparatus constructed in accordance with the principles of theinvention;

Figure 2 is a partial side elevation of the structure shown in Figure 1;

Figure 3 is a rear elevation of Figure 2;

Figure 4 is a rear elevation corresponding to Figure 3, but illustratinga modified form of the invention applicable to twin screw propelledvessels;

Figure 5 is a horizontal section of a preferred form of rudder element;and

Figures 6, '7, and 8 are vertical sections taken substantially on thelines 6-45, 'l!, and 8-8, respectively, of Figure 5.

In order to facilitate an understanding of the invention, reference willbe made to the several embodiments thereof illustrated in theaccompanying drawing and specific language will be employed. It willnevertheless be understood that various further modifications of thedevices illustrated herein, such as would fall within the province ofthose skilled in the art to con struct, are contemplated as part ofthepresent invention.

The invention is particularly effective when applied to shallow draftvessels, and is so illustrated in the drawing. Thus, referring to Figure2 of the drawing, it will be observed that the hull It is provided witha bottom which rises at the stern, as indicated at I l, to accommodatethe propeller IS, the propeller shaft being indicated at Ill. Thepropulsion system forms no part of the instant invention, except incombination with the steering system hereinafter described. and maytherefore be modified as desired.

The steering system consists essentially of spaced rudders l6 and I1,disposed at opposite sides of the propeller I3 and in contiguousrelation therewith. The rudders are illustrated as balanced, and extendboth forwardly and rearwardly from the respective pivotal axes thereof,as defined by the usual rudder stems l8 and [9, the latter being rigidwith the rudders.

The pair of rudders are connected for conjoint steering movement by anyconvenient means, the details of which form no part of the instantinvention. For example, a worm gear sector may be secured to each rudderstem, these sectors being indicated at 22 and 23 respectively, and atransversely extending shaft 25 may be provided 1 at its opposite endwith worms 26 and 21 meshing respectively with the sectors 22 and 23.The shaft 25 may be rotated through bevelled gears 28 and O 29 by thesteering shaft 3|, to which is secured the usual wheel 30.

The configuration of the rudders l6 and I! in elevation is notimportant, although I prefer to form them as shown in Figure 2. Theoutwardly facing surface of each rudder is preferably flat, defining aplane substantially parallel to the rudder axis; the planes thus definedby the pair of rudders are generally parallel to each other.

The opposed or inner facesof the rudders are shaped as shown moreparticularly in Figures 5 to 8, inclusive.

Thus the intermediate part of the inner face of rudder [6, indicated at33 in Figure 5, conforms generally to a surface of revolution of whichthe axis of generation is coincident with the axis of rotation of therudder, the generatrix being constituted by an arc of a circlesubstantially concentric with the circle described by the propeller tipsand of somewhat greater radius, the difference in radius being at leastsufficient to afford adequate clearance between the rudders and thepropeller tips. It will be appreciated that as the rudders are rotatedabout their respective steering axes, the area enclosed between them inthe plane of the propeller will remain substantially constant, and theclearance for the propeller tips will remain constant, the shape of thearea being unchanged. As shown in Figure 3, the surface of revolutionjust described is of substantial extent, measured in a verticaldirection, so as to extend both above and below the horizontal planecontaining the propeller axis and partially surround the propeller, Theextent of this surface of revolution, measured longitudinally of thevessel, is preferably suificient to maintain constant clearance with thepropeller when the helm it put over in either direction to its extremeangle.

Alternatively, the intermediate part of the inner face of the rudder maybe described as of such contour that generally horizontal sectionsdefine circular arcs about the axis of the rudder stem, whereas atransverse generally vertical section through the rudder stem defines acircular are about the propeller axis having a radius greater than thepropeller tip radius.

As hereinbefore pointed out, it is extremely important, in order tosecure the highest operating efficiency in either direction of motion ofthe vessel, that the inner faces of the rudders diverge forward and aftof the propeller. With this end in view, and in order to secure optimumflow conditions, the surfaces at the intermediate parts of the ruddersare gradually flattened in each direction from the propeller andpreferably merge, adjacent the rudder tips 34 and 35, into divergentplane surfaces. The curvature of the inner face of each rudder invertical planes thus gradually decreases both fore and aft of the rudderstem, as illustrated more particularly in Figures 6, 7, and 8 of thedrawing. The area defined between the rudder tips both fore and aftshould be sufficient, as hereinbefore indicated, to compensate forcontraction of v the propeller race resulting from normal accelerationin the direction of and deceleration away from the propeller. In otherwords, the divergence of the inner surfaces ofthe rudders away from thepropeller in each direction should be at least sufficient to preventsubstantial cavitation regardless of the direction in which the vesselis proceeding.

For convenience in illustrating the invention, the propeller shaft isshown in a horizontal position. In the event the invention is applied tocraft in which the propeller shaft is inclined, some correspondingmodification of the disposition of the rudder surfaces may be desirablein order to attain maximum efliciency. It is intended that all ordinarydeviations of the propeller shaft from a true horizontal are comprisedwithin the scope of the term generally horizontal.

In the modified form shown in Figure 4, applicable to Vessels propelledby twin screws, the two outer rudders 40 and 4| may be shaped ashereinbefore described. The rudder 42, intermediate the propellers, isformed on both its surfaces as described hereinbefore with reference tothe inner surfaces of rudders l6 and I1. Thus the propeller race isdirected toward and awai from each of the propellers 44 and 45 inprecisely the same manner as in the embodiment first described, Suitablemeans, not shown, may be provided for effecting concurrent rotation ofall three rudders.

It will be appreciated that by the arrangement described, the propellerrace is so controlled and directed inits movement toward and away fromthe propellers that losses due to lateral deflection of the race andturbulent fiow may be materially reduced. This is especially true in thecase of vessels proceeding in water of shallow draft, where the bottomcooperates to a certain extent with the rudders and with the vesselbottom to confine the propeller race rather closely to a prescribed pathaffording optimum operating conditions. The flaring inlet and outletoffers little resistance to flow and inhibits the suction or draw of thewater to the propeller from the side, thus increasing the tractiveeffort. The tendency of the vessel to squat when in shallow water isaccordingly materially reduced. The steering apparatus herein describedis found to give greatly increased response, particularly for smallangles of helm, and thus the water channel remains practically constantand is properly directed to the propeller regardless of the sharpness ofangle through which the vessel is turned or of the direction in whichthe vessel is propelled.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. In steering apparatus for screw propelled vessels, the combinationwith a propeller, of balanced rudders, one disposed at each side of saidpropeller, means supporting said rudders for pivotal and concurrentmovement about upstanding axes disposed in a common plane generallyperpendicular to the propeller axis, each of said rudders having anintermediate part of the inner face thereof formed as a portion of asurface of revolution of which the generating axis is substantiallycoincident with the rudder axis, and of which the generatrix is an arcof a circle substantially concentric with the circle described by thepropeller tips and of slightly greater radius, the inner faces of therudders diverging forward and aft from the said intermediate partsthereof to an extent sufficient to permit required acceleration anddeceleration of the propeller race without disturbing loss due tocavitation in either forward or reverse direction of movement of thevessel.

2. In steering apparatus for screw propelled vessels, the combinationwith a propeller, of balanced rudders, one disposed at each side of saidpropeller, means supporting said rudders for pivotal and concurrentmovement about upby the propeller tips and of slightly greater radius,the inner faces of the rudders diverging forward and aft from thesaidintermediate parts thereof to an extent sufficient to permitrequired acceleration and deceleration of the propeller race withoutdisturbing loss due to cavitation in 3 either forward or reversedirection of movement of the vessel, the outer faces of the ruddersdefining substantially parallel planes.

3. In steering apparatus for screw propelled vessels, the combinationwith a propeller, of a pair of rudders, one disposed at each side ofsaid propeller, means supporting said rudders for pivotal and concurrentmovement about upstanding axes disposed in a common plane generallyperpendicular to the propeller axis, each of said rudders having a partof the inner face thereof formed as a portion of a surface of revolutionof which the generating axis is substantially coincident with the rudderaxis, and of which the generatrix is an arc of a circle substantiallyconcentric with the circle described by the propeller tips and ofslightly greater radius.

4. In steering apparatus for screw propelled vessels, the combinationwith a propeller, of a pair of rudders, one disposed at each side ofsaid propeller, means supporting said rudders for pivotal and concurrentmovement about upstanding axes disposed in a common plane generallyperpendicular to the propeller axis, each of said rudders having a partof the inner face thereof formed as a portion of a surface of revolutionof which the generating axis is substantially coincident with the rudderaxis, and of which the generatrix is an arc of a circle substantiallyconcentric with the circle described by the propeller tips and ofslightly greater radius, the outer faces of the rudders definingsubstantially parallel planes.

5. In steering apparatus for screw propelled vessels, the combinationwith a propeller, of a pair of rudders, one disposed at each side ofsaid propeller, means supporting said rudders for pivotal and concurrentmovement about upstanding axes disposed in a common plane generallyperpendicular to the propeller axis, each of said rudders having a partof the inner face thereof formed asa portion of a surface of revolutionof which the generating axis is substantially coincident with the rudderaxis, and. of which the generatrix is an arc of a circle substantiallyconcentric with the circle described by the propeller tips and ofslightly greater radius, said surface extending a substantial distanceabove and below the generally horizontal plane containing the propelleraxis.

6. In steering apparatus for screw propelled vessels, the combinationwith a propeller, of balanced rudders, one disposed at each side of saidpropeller, means supporting said rudders for pivotal and concurrentmovement about upstanding axes disposed in a common plane generallyperpendicular to the propeller axis, each of said rudders having anintermediate part of the inner face thereof formed as a portion of asurface of revolution of which the generating axis is substantiallycoincident with the rudder axis, and of which the generatrix is an arcof a circle substantially concentric with the circle described by thepropeller tips and of greater radius, the inner faces of the ruddersdiverging forward and aft from the said intermediate parts thereof to anextent sufiicient to permit required acceleration and deceleration ofthe propeller race without disturbing loss due to cavitation in eitherforward or reverse direction of movement of the vessel, said propellerbeing unconfined over a substantial part of the lower portion of thepath traced out by the propeller tips.

RICHARD NEWELL COOLIDGE.

